Your processor and RAM are good to go. I don't know enough about the graphics card to know how well it will run SH4 except that we have people on the board using it that are happy.
The message of GWX is "you are going to die." The palpable feeling of doom is not present in SH4. Here you have a feeling that you should survive to see the end of the war. This has the effect of making you bolder and more likely to die stupidly.
It also makes attacks by escorts more trying for me, as I tend to treat it as an impediment to my hunting activity--a bother, really.
Actually, the two games are so different that it becomes difficult to compare the quality. Both have some defects that can cross them off your list. SH3/GWX, for existance, ignores the essential factor of cooperation between U-Boats in a wolfpack, and so is in no way a realistic simulation of the U-Boat experience. Taken from that observation, SH4 is far superior because the individual boat's operation is just as faithfully executed as SH3.
I think the games compliment each other. Having both makes me appreciate each one more than I did when I only had one. Once I complete my SH4 career I'm going to try again at SH3/GWX2 if I can get the save game glitch under control this time. In saving games, SH4 is clearly very superior to SH3.